Some conventionally known vehicle lighting fixtures used as a rear lamp or a position lamp include a light source such as a light emitting diode (LED) and a light guiding lens having a reflective function portion and a light exiting surface. In this type of lighting fixtures, light emitted from the light source can enter the light guiding lens and be guided by the reflective function portion thereof in its longitudinal direction. During the guiding of light, the light can be reflected, thereby exiting through the light exiting surface. In this case, there may be formed a plurality of lens cuts in a surface of the light guiding lens opposite to the light exiting surface.
In a vehicle lighting fixture including such a light guiding lens, there is a large difference in luminance between a nearer position and a farther position from the light source, resulting in decreased uniform luminance in the light exiting surface.
In order to cope with this problem, there has been proposed a vehicle lighting fixture including a light guiding lens as shown in FIG. 1, for example, those disclosed in Japanese Patent Application Laid-Open No. 2013-045671.
FIG. 1 is a cross-sectional view illustrating part of a light guiding lens 101 of the vehicle lighting fixture proposed in Japanese Patent Application Laid-Open No. 2013-045671. The light guiding lens 101 is configured to include a plurality of prism cuts 101a formed in a surface (lower surface in FIG. 1) opposite to a light exiting surface (upper surface in FIG. 1) on a side near a not-illustrated light source and curved surfaces 101b concavely formed between the prism cuts 101a configured such that the respective curved surfaces 101b connect the adjacent ones of the prism cuts 101a. 
In the light guiding lens 101 with such a configuration, light from the light source can be diffused by the curved surfaces 101b to reach the farther side of the light guiding lens 101 and be totally reflected within the light guiding lens 101. Then, the light diffused and/or reflected can be controlled by the prism cuts 101a in terms of light distribution so as to be projected through the light exiting surface of the light guiding lens 101 (upper surface in FIG. 1). Accordingly, the difference in luminance between the nearer position and the farther position from the light source can be reduced to improve the uniformity in luminance in the observed light exiting surface of the vehicle lighting fixture. The formation of such curved surfaces 101b concavely formed between the adjacent prism cuts 101a can properly diffuse the bundle of light rays to provide a light projection state with even luminance.
In the vehicle lighting fixture including the light guiding lens 101 as illustrated in FIG. 1, although the difference in luminance between the nearer position and the farther position from the light source can be reduced, the light projection is monotonous due to the uniform projection of light with a wider angle range of the light guiding lens 101, resulting in decrease of luxurious feeling as a vehicle lighting fixture.